Method for dirtproofing treatment for plastic lens

ABSTRACT

A method is disclosed which concerns the treatment for imparting dirtproofness to a plastic lens provided in advance on the surface thereof with an antireflection film formed by vacuum evaporation of an inorganic substance. This method forms a dirtproofing film on the antireflection film by mixing a polyfluoroalkyl silane-containing coating liquid and trichlorotrifluoroethane and boiling the resultant mixture, dip coating the plastic lens in the boiled mixture, then treating the dip coated plastic lens with the vapor of fluoroethane, subsequently drying the wet plastic lens with hot air, and optionally immersing the dried plastic lens in water.

TECHNICAL FIELD

This invention relates method of treatment for imparting a dirtproofingproperty (inclusive of waterproofing property and oilproofing property)to a plastic lens having a film of an inorganic substance deposited byvacuum evaporation on the surface of a substrate. It is particularlyadvantageous for application to an eyeglass.

BACKGROUND ART

In the substrates for plastic lenses, particularly transparentsubstrates reflect beams of light from the sun or the illumination andsuffer from loss of transmittance of light. Owing to this loss oftransmittance, a light passed through a lens loses in brightness. Thereflection of light produces a reflected image called a ghost on thelens surface and imparts an unpleasant feeling to the eyes of the personwearing the lens. In the plastic substrates, the eyeglass lens isdeficient in surface hardness and liable to sustain scratches. For thealleviation of the impacts of these drawbacks, the practice of coatingthe eyeglass lens with a film, particularly an antireflection film, ofan organic substance by vacuum evaporation is in vogue.

When the antireflection film is covered with electrostatically depositeddirt and dust or with physically deposited filth, fingerprints, andperspiration from hands, it is misted possibly to the extent ofobstructing the vision of the person wearing the eyeglass and compellingthe person to experience an unpleasant feeling. In the circumstances,wiping cloth and paper and detergents useful for temporary removal ofdirt are offered in the market. Methods for imparting a dirtproofingproperty to the antireflection film by applying a substance containingan organic silicon compounds on the film have been disclosed in JapanesePatent Application Disclosures SHO 61(1981)-130,902, SHO 51(1976)-1,387,and SHO 50(1975)-10,440, for example. The conventional methods effectthe surface treatment by employing the dip coating method and attain thedrying of a wet applied layer by allowing the wet layer to standovernight at normal room temperature or to stand for not less than 20minutes at a temperature of about 100° C. Thus, they invariably requirethe wet applied layer to be dried by standing either for a long time orat an elevated temperature.

The conventional dirtproofing treatment of a lens resorting to the dipcoating method has a disadvantage that the film formed by vacuumevaporation is liable to sustain cracks in the surface, through whichthe lens suffer from impairment of its appearance, because the wetapplied film has to be dried by a protracted standing at an elevatedtemperature approximately in the range of 50° C. to 70° C. or by a briefstanding at higher temperature approximately in the range of 70° C. to100° C. The protracted standing for the purpose of drying is nothingdesirable from the standpoint of productivity.

The dip coating method is popularly used for the treatment underdiscussion. The conventional dip coating method has a disadvantage thatthe applied liquid layer tends to leave a mark of drawdown on the lenssurface and form a dry layer of uneven wall thickness. If the drawdownblurs the lens surface, the mark of blur stands out and spoils theappearance of the lens.

The polyfluoroalkyl silane which is used as an organic silicon comoundfor the dirtproofing treatment is so expensive that generous use of thiscompound is undesirable from the standpoint of cost.

DISCLOSURE OF INVENTION

The inventors studied the problem mentioned above from various anglesand continued a diligent study in search of a method of treatment forimpartation of dirtproofness and scratchproofness to the film depositedby vacuum evaporation. They has consequently conceived the followinggeneral idea about a method for the dirtproofing treatment of a plasticlens.

To be specific, this invention concerns a method for the impartation ofdirtproofness to a plastic lens provided with an antireflection filmdeposited by vacuum evaporation. This method is characterized by thesteps of mixing a polyfluoroalkyl silanecontaining coating liquid withtrichlorofluoroethane, boiling the resultant mixture, dip coating agiven plastic lens with the boiled liquid, then treating the coatedplastic film with the vapor of trichlorotrifluoroethane, subsequentlydrying the wet plastic lens with hot air, and optionally cleaning thedried plastic lens by immersion in water thereby giving rise to adirtproofing film on the antireflection film.

The method of this invention for the dirtproofing treatment of a plasticlens permits removal of a mark possibly left on an eyeglass lens by thesuction plate to be used during the grinding work. The lens treated bythis method enjoys good appearance unlike the plastic lens treated bythe conventional method because it does not allow a mark of the suctionplate, a mark of drawdown inflicted during the course of dip coating, ora mark of stain due to lack of uniformity of applied layer to stand outwhen the lens surface is misted. Moreover, this lens does not permitready adhesion of such defiling matter as fingerprints and filth fromhands but permits ready removal of dirt with dry cloth or paper. Unlikethe lens yet to be treated, the lens treated by the method of thisinvention defies opacification with the grease of fingerprints, forexample, keeps transparency intact. It ruther enjoys satisfactoryslidability of surface and, therefore, offers resistance to inflictionof scratches. It has an ability to repel water and oil and keep itssurface free from raindrops on a rainy day. By the test forweatherability, the treates lens has been confirmed to retain thedesirable effects mentioned above for a long time. The method of thisinvention produces these desirable effects on the plastic lens by atreatment to be given at a low temperature approximately in the range of40° C. to 60° C. for a short period on the order of 10 minutes. Thus,the method enjoys high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating in model the relation of componentlayers of a plastic lens after the dirtproofing treatment.

BEST MODE FOR CARRYING OUT THE INVENTION

As typical examples of the polyfluoroalkyl silane to be used in thepresent invention, the following compounds may be cited.

CF₃ CH₂ CH₂ Si(OCH₃)₃

CF₃ (CF₂)₃ CH₂ CH₂ Si(OCH₃)₃

CF₃ (CF₂)₅ CH₂ CH₂ Si(OCH₃)₃

CF₃ (CF₂)₇ CH₂ CH₂ Si(OCH₃)₃

CF₃ CH₂ CH₂ Si(OC₂ H₆)₃

CF₃ (CF₂)₃ CH₂ CH₂ Si(OC₂ H₅)₃

CF₃ (CF₂)₅ CH₂ CH₂ Si(OC₂ H₅)₃

CF₃ (CF₂)₇ CH₂ CH₂ Si(OC₂ H₅)₃

CF₃ CH₂ CH₂ SiCl₃

CF₃ (CF₂)₃ CH₂ CH₂ SiCl₃

CF₃ (CF₂)₅ CH₂ CH₂ SiCl₃

CF₃ (CF₂)₇ CH₂ CH₂ SiCl₃

CF₃ (CF₂)₅ CH₂ CH₂ SiCH₃ Cl₂

CF₃ (CF₂)₇ CH₂ CH₂ SiCH₃ Cl₂

CF₃ (CF₂)₅ CH₂ CH₂ SiCH₃ (OCH₃)₂

CF₃ (CF₂)₇ CH₂ CH₂ SiCH₃ (OCH₃)₂

CF₃ (CF₂)₅ CH₂ CH₂ SiCH₃ (OCH₅)₃

CF₃ (CF₂)₇ CH₂ CH₂ SiCH₃ (OC₂ H₅)₃

The polyfluoroalkyl silane solution to be used herein as the treatingliquid is prepared by mixing the polyfluoroalkyl silane in an amount inthe range of 1 to 10 wt% with a lower alcohol as a solvent andhydrolyzing the resultant mixture. The polyfluoroalkyl silane is soexpensive that ample use thereof is undesirable from the economic pointof view. In the treatment by the dip coating method, since the wetapplied layer is dried at a temperature not exceeding 60° C., sole useof a lower alcohol tends to entail the phenomenon of drawdown and heavyloss of the treating liquid by entrainment. To preclude this trouble,one part by weight of the polyfluoroalkyl silane solution which hasundergone the hydrolysis with a lower alcohol is used as diluted in 2 to10 parts by weight of trichlorotrifluoroethane which has a low boilingpoint and exhibits high solubility in the low alcohols. Typicalproprietary products of trichlorotrifluoroethane are Daifron Solvent S3(trademark designation owned by Daikin Kogyo Co., Ltd.), Fronsolve(trademark designation owned by Asahi Glass Company, Ltd.), and Freon TF(trademark designation owned by Mitsui-DuPont Fluorochemical K.K.), forexample. In preparation for the treatment by the dip coating method, thediluted polyfluoroalkyl silane-containing solution is heated to andboiled at the boiling point (about 47° C.). In the boiling solution, agiven substance is kept immersed for about one minute. This substrate isdesired to have been deprived of such defiling matters as fingerprintsand filth from hands and saliva deposited on the film of vacuumevaporation. The boiling tank to be used for the dip coating is desiredto be a vapor tank provided with a condenser. The substrate immersed isdip coated in the bath. While the dip coated substrate is being liftedfrom the bath, it is caused to pass through the vapor oftrichlorotrifluoroethane having a pressure of 1 kg/cm² abs. Thus, auniform coating is formed on the substrate. The coated substrate is thenplaced in a hot air tank and dried therein under the conditions of 40°C. to 60° C.×1 to 5 minutes. If this drying is continued for a longertime or carried out at a temperature exceeding 60° C., it possiblyentails a disadvantage that the film of vacuum evaporation will sustaincracks on the surface and acquire a spoiled appearance. To enhancefurther the effect of the dirtproofing treatment, the coated lens afterthe drying in hot air is immersed in water for two to five minutes. Thisimmersion is advantageous because it is effective in removing theunaltered monomer and uniformizing the film.

If the produced film is deprived of the uniformity of wall thickness bythe dirtproofing treatment, then the interference fringes and thereflection colors consequently produced will eventually impair thequality of the film of vacuum evaporation. By washing the coated lens ina dehtdrating tank, a trichlorotrifluoroethane tank, an alcohol tank,etc., the film can be finished in an extremely small and uniform wallthickness without any sacrifice of quality. It has been demonstrated asin Japanese Patent Application disclosure SHO 61(1986)-130,902, forexample, that the film of a wall thickness not exceeding 100 Å has nobearing on the impact of interference fringes. Actually the surface ofthe film formed by vacuum evaporation is full of extremely minute risesand falls and pits. Since these surface irregularities admit thepolyfluoroalkyl silane, the film is finished advantageously in anextremely small wall thickness. The polyfluoroalkyl silane thus lodgedin the surface portion of the film presumably serves to smoothen thefilm surface enough for the finished film to exhibit highly satisfactoryslipperiness.

Generally the film formed by vacuum evaporation yields its quality tothe impact of aging and tends to lose in thermal stability andwaterproofness with elapse of time. The treatment to be performed afterthe dip coating treatment, therefore, is desired to be completed withina short span of time. The film of vacuum evaporation which has beengiven this treatment has a surface which is not easily defiled andpermits ready removal of adhering dirt and, moreover, excels inwater-repellency and oil-repellency. This film has an additionaladvantage that the surface thereof enjoys highly satisfactoryslipperiness and defies infliction of cracks. It retains dirtproofness,water-repellency, and oil-repellency intact through a protracted use.These merits warrant effective application of the invention to plasticlens and particularly an eyeglass lens.

The time required for the dirtproofing treatment by the method of thisinvention is roughly 10 minutes, a duration which is one half of thetime required for the treatment by the conventional method. Thus, thistreatment enjoys proportionately high productivity.

EXAMPLES

Now, the present invention will be described more specifically belowwith reference to working examples. It should be noted, however, thatthis invention is not restricted by these examples. Preparation oftreating liquid:

In 100 parts by weight of methanol, 5 parts by weight of polyfluoroalkylsilane represented by the following structural formula:

    CF.sub.3 (CF.sub.2).sub.7 CH.sub.2 CH.sub.2 Si(OCH.sub.3).sub.3

was dissolved. The resultant solution was placed in a three-neck flaskand stirred and refluxed for hydrolysis at the temperature of 82° C. fortwo hours. After the reflux, the hydrolyzate and 400 parts by weight ofDaifron Solvent S3 (trademark designation owned by Daikin Kogyo Co.,Ltd.) added thereto were toroughly stirred to produce a 1% solution ofpolyfluoroalkyl silane.

EXAMPLE 1

On a plane lens of CR39 (polydiethylene glycol bisallyl carbonate) 70 mmin diameter, an antireflection film was formed by sequentiallysuperposing SiO₂, ZrO₂, Al₂ O₃, ZrO₂, and SiO₂ in respective thicknessesof λ/4, λ/8, λ/8, λ/4, and λ/4 (λ=520 mm) (seeing FIG. 1) in the ordermentioned from the lens surface side by the method of vacuumevaporation. The film assumes a reflection interference color of green.The dirtproofing treatment was carried out by boiling the treatingliquid mentioned above, keeping the substrate immersed in the boilingtreating liquid for one minute, and lifting the substrate at a rate of 3m/min to complete the dip coating treatment. Since the dip coatedsubstrate was necessarily passed through the vaper of Daifron Solvent S3(trichlorotrifluoroethane) (1 kg/cm² abs) at 47° C., a uniform film wasformed thereon without entailing the phenomenon of drawdown. The coatedsubstrate was then dried for one minute in an atmosphere kept at 60° C.and then kept immersed in water for five minutes. As the result, thefilm of polyfluoroalkyl silane was solidified on the surface of theantireflection film. The substrate still wet was dehydrated, washed withDaifron Solvent S3 for removal of loose fragments from the film surface.The solid film produced in a small uniform thickness not exceeding 100 Åwas finished in a Daifron solvent S3 vapor tank (1 kg/cm² abs) kept at47° C.

Comparative Experiment 1

In the same manner as in Example 1, an antireflection film was formed ona lens of CR39. The same treating liquid was cooled to 10° C. The lenswas immersed in the cooled treating liquid and lifted from the bath at arate of 3 m/min to effect dip coating.

Comparative Experiment 2

A treating liquid was prepared by following the procedure of Example 1up to the step of hydrolysis and omitting the subsequent step ofdilution with Daifron Solvent S3. This treating liquid was cooled to 10°C. A given lens was immersed in the cooled treating liquid and thenlifted from the bath at a rate of 3 m/min to effect dip coating.

When the treatment was carried out by this procedure, the treatingliquid applied on the lens surface was not easily vaporized and causedthe phenomenon of drawdown. Thus, no uniform coating could be obtained.Moreover, the polyfluoroalkyl silane was heavily lost by being entrainedby the treated substrate.

Comparative Experiment 3

The procedure of Experiment 1 was repeated, excepting the treatment withwater (five minutes immersion in water) was omitted, the hot air dryingwas continued for five minutes, the washing was made with DaifronSolvent S3, and the washed substrate was finished with the vapor of thesolvent (1 kg/cm² abs).

Comparative Experiment 4

The procedure of Embodiment 1 was repeated, excepting the time for thehot air drying was changed to one minute.

Comparative Experiment 5

On a CR39 plane lens 70 mm in diameter, an antireflection film wasformed by following the procedure of Embodiment 1. It was not subjectedto the dirtproofing treatment.

The plastic lenses obtained in the embodiment and the comparativeexperiments described above were evaluated with respect toscratchproofness, dirtproofness, and appearance by the respectivemethods indicated below. The results are shown in Table 1.

(1) Scratchproofness

This property was determined by rubbing the surface of a given sampleplastic lens with a 3-cm cube of steel wool (0000) held in a hand andpressed against the surface with a fixed strength determined by ratingthe extent of scratches inflicted by the rubbing on rhe surface andrating the scratches formed on the surface on the three-point scale,wherein A stands for infliction of slight (shallow) scratches, B forinfliction of rather deep scratches, and C for infliction of heavyscratches.

(2) Dirtproofness

This property was determined by keeping a sample plastic lens in hotwater at 80° C. for 10 minutes, wiping the wet lens surface with a wadimpregnated with acetone, placing water drops on the cleaned lenssurface, drying the lens with hot air at 60° C. for ten minutes, andthen trying the dried surface of the lens to find whether or not anywater mark or smear could be easily removed by rubbing. The rating wasmade on the three-point scale, wherein a double circle ( ⊚ ) stands forready removal with dry cotton cloth, a single circle ( ○) for ratherforced removal with dry cotton cloth, and a cross (×) for unsuccessfulremoval (water mark persisting in white around the boundary afterrubbing with cotton cloth impregnated with acetone).

(3) Appearance

This property was determined by wiping the surface of a sample lensclean with a wad impregnated with acetone, fogging the cleaned lenssurface with breath, observing the fogged lens surface against the lightfrom a fluorescent lamp, and rating the mark of drawdown or othersimilar mark on the three-point scale, wherein X stands for absence ofany discernible mark of fogging with breath, Y for presence of barelydiscernible mark of fogging with breath, and Z for presence of clearlydiscernible mark of fogging with breath.

Example 2

A plane lens of polycarbonate resin was subjected to hard coating withan organic substance. On the hard film consequently formed on the lens,a film was formed by sequentially superposing layers of SiO₂, ZrO₂,SiO₂, ZrO₂, ZrO₂, SiO₂, ZrO₂, and SiO₂, in respective thicknesses ofλ/4, λ/4, λ/4, λ/4, λ/4, λ/4, and λ/2 (λ=520 mm) in the order mentionedfrom the lens surface side by vacuum evaporation. The lens was subjectedto the same dirtproofing treatment as in Example 1. The film of vacuumevaporation possessed satisfactory slipperiness and exhibited highdirtproofness.

                  TABLE 1                                                         ______________________________________                                                Scratchproofness                                                                         Dirtproofness                                                                            Appearance                                      ______________________________________                                        Example 1 A            ⊚                                                                         X                                           Comparative                                                                             A            ⊚                                                                         Y                                           Experiment 1                                                                  Comparative                                                                             B            ○   Z                                           Experiment 2                                                                  Comparative                                                                             A            O          X                                           Experiment 3                                                                  Comparative                                                                             B            X          X                                           Experiment 4                                                                  Comparative                                                                             B            X          X                                           Experiment 5                                                                  ______________________________________                                    

We claim:
 1. A method for the impartation of dirtproofness to a plasticlens provided in advance of a film formed by vacuum evaporation, whichmethod comprises the steps of:(a) mixing a polyfluoroalkylsilane-containing coating liquid and trichlorotrifluoroethane in agravimetric ratio in the range of 1/2 to 1/10 and boiling the resultantmixture, (b) subjecting said plastic lens to a dip coating treatment inthe boiled mixture, and (c) removing said plastic lens from said boiledmixture and dried with hot air under the conditions of 1 to 5minutes×40° C. to 60° C. thereby forming a dirtproofing film on saidfilm of vacuum evaporation.
 2. A method according to claim 1, whichfurther comprises a step of immersing in water the plastic lens aftersaid step of drying with hot air.
 3. A method according to claim 1 orclaim 2, wherein a hard coat is interposed between said substrate andsaid film of vacuum evaporation.